The use of inkjet printing systems has grown dramatically in recent years, which is attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Notwithstanding their recent success, intensive research and development efforts continue toward improving inkjet print quality, while further lowering cost to the consumer.
With inkjet printing, a desired printed image is formed when a precise pattern of dots is ejected from a drop-generating device, known as a printhead, onto a print medium. The printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an inkjet printhead substrate. The inkjet printhead substrate incorporates an array of firing chambers that receive inkjet ink through fluid communication with one or more ink reservoirs. Each firing chamber has a resistor element, known as a firing resistor, located opposite the nozzle so that the inkjet ink collects between the firing resistor and the nozzle. Each resistor element is typically a pad of a resistive material and measures about 35 μm×35 μm. The printhead is held and protected by an outer packaging referred to as a print cartridge or an inkjet pen. Upon energizing of a particular resistor element, a droplet of inkjet ink is expelled through the nozzle toward the print medium. The firing of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements, forming alphanumeric and other characters on the print medium. The small scales of the nozzles, which are typically 10 μm to 40 μm in diameter, require that the ink does not clog the nozzles. However, repeated firings of the resistor elements, which are designed to withstand millions of firings over the life of the print cartridge, result in fouling of the resistor elements with residue and degradation of pen performance. This build up of residue is known as kogation. The term “kogation” is, thus, used herein to refer to the buildup of the residue, or koga, on a surface of the resistor element in the inkjet pen.
To produce high quality images, the inkjet ink has to be compatible with the inkjet pen and the print medium. In addition, the ink has to be capable of passing through the inkjet orifice without clogging the orifice plate.
Inkjet ink typically includes one or more colorants dissolved or dispersed in an aqueous-based ink vehicle and can also contain anti-kogation components. Such anti-kogation components have been used to counter the kogation effect. However, such components tend to be not stable in the ink composition and often precipitate. Such precipitation phenomenon results in a deposition phenomenon which tend clog the nozzle of the print head
Clogging of ink occurs when ink drops, exiting the orifices, leave behind minute amounts of ink on the orifice plate around each orifice. The inkjet ink collects on an outer surface of the orifice plate or puddles adjacent to the edge of the orifice. Such clogging happens at the fore end of the narrow nozzle so that the direction and quantity of ink jetted become unstable. This clogging effect results in that the size and the speed of ink drops vary exceedingly whereby it becomes impossible to obtain a clear record and jet printing is hampered. This phenomena result thus in poor printing performances.
Clogging naturally happen on inks, however, this phenomenon is accentuated by precipitation of some components of ink composition, such as anti-kogation components, and furthermore, is accentuated when metal ions contaminate ink composition.
It has thus often created challenges to formulate ink compositions which do not have a kogation effect and which do not result in clogging the nozzle of the printing machine; in other words, which can be effectively used with inkjet printing techniques and which provide good image printing performances.